1. Field of the Invention
The present invention relates to an outboard motor provided with an improved mount structure for mounting the outboard motor to a hull, for example.
2. Discussion of the Background
FIG. 4 shows one example of an outboard motor 1 which is generally mounted to a hull H (transom) through a bracket 6, to which support members such as upper and lower mount devices 20 and 21 are mounted at vertically two portions in an installed state of the outboard motor to the hull.
Usually, when an engine 3 of the outboard motor is fully driven, the mount devices 20 and 21 may be displaced because of, for example, vibration of the engine 3 and such displacement is restricted by interposing a thrust stopper 23, as another support member, made of an elastic material such as rubber between the body (casing) of the outboard motor 1 and the bracket 6. The thrust stopper 23 is arranged at a level substantially equal to that of the lower mount 21 in a conventional structure.
With reference to FIG. 4, a load applied to the upper and lower two mount devices 20 and 21 will be expressed by the following equations.
F2pri(load applied to the lower mount device 21)={(L1+L2)/L2}xc3x97F1pri
F3pri(load applied to the upper mount device 20)=L1xc3x97F1pri/L2=F1prixe2x88x92F2pri
wherein F1pri is a propelling force of a propeller 13, L1 is a distance between an axis of the propeller 13 and an axis of the lower mount device 21 and L2 is a distance between the axes of the upper and lower mount devices 20 and 21.
Incidentally, in a two-stroke-cycle two-cylinder engine or four-stroke-cycle three- or five-cylinder engine, an inertia couple of force is generated about a center of a crankshaft 4 of the engine and the inertia couple of force generates a vibration about a center of gravity C/G of the engine 3. In the outboard motor 1, as shown in FIG. 4, the center of gravity C/G is generally positioned at a portion near the upper mount device 20 disposed at an upper position of the central portion of the entire structure of the outboard motor 1. Further, in the outboard motor 1, primary and secondary vibrations or like of the engine 3 other than the vibration due to the inertia couple of force mentioned above are generated in a complicated manner, thus providing a problem.
A thrust stopper 23 is disposed for the purpose of preventing an excessive deviation of the lower mount device 21 and arranged in a level substantially equal to the lower mount device 21. When the lower mount device 21 is arranged at a lower position, it supports the engine 3 at a position apart from the center of gravity C/G of the engine 3, and hence, it is difficult to absorb the vibration of the engine 3 due to the inertia couple of force mentioned above.
In such a positional arrangement, when the lower mount device 21 is located at a high position, the load Fpri applied to the upper mount device 20 at the engine full operation time, for example, is made large and it is necessary to construct the upper mount device 20 by using a relatively hard elastic material.
However, in a case when the upper mount device 20 is formed of a relatively hard elastic material, the upper mount device 20 will not sufficiently absorb the complicated primary and secondary vibrations of the engine 3.
An object of. the present invention is to substantially eliminate defects or drawbacks encountered in the prior art mentioned above and to provide an outboard motor having an improved mount structure capable of effectively reducing the load applied to the mount devices at a time of fully operating the engine of the outboard motor.
This and other objects can be achieved according to the present invention by providing an outboard motor which comprises:
an engine holder;
an engine disposed above the engine holder in a state wherein the outboard motor is mounted to a hull;
a mount unit including upper and lower mount devices for mounting the outboard motor to the hull and a bracket through which the upper and lower mount devices are mounted to the hull;
an elastic member disposed between the bracket and a body of the outboard motor; and
a propeller driven in accordance with the engine operation,
wherein the distance between an axis of the upper mount device and an axis of the elastic member both extending in a direction parallel to an axis of the propeller is set to be larger than the distance between axes of the upper and lower mount devices which extend in a direction parallel to the axis of the propeller.
In a preferred embodiment, the elastic member is positioned such that the axis of the elastic member is below the axis of the lower mount device. The bracket is provided with a downward extension, to which the elastic member is provided. The elastic member may be formed as a thrust stopper.
According to the present invention of the characters mentioned above, the distance between an axis of the upper mount device and the axis of the elastic member both extending in the direction parallel to the axis of the propeller is set to be larger than the distance between the axes of the upper and lower mount devices which extend in a direction parallel to the axis of the propeller, so that the load to be applied to the upper mount member can be reduced and the vibration of the entire structure of the outboard motor can be also reduced. Furthermore, these advantageous effects can be further increased according to the arrangement of the preferred embodiment mentioned above.
The nature and further characteristic features of the present invention will be made further clear from the following descriptions made with reference to the accompanying drawings.